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Any of those alluvial valleys would meet the regulatory definition of an alluvial valley floor <br /> (AVF) if the valleys had water availability sufficient for flood-irrigated agricultural activities <br /> [Section 1.04(10)1, or availability of water sufficient for sub-irrigated agricultural activities <br /> [Section 1.04(10)]. Flood irrigation is practiced on the valley floors of the Yampa River in the <br /> Big Bottom area and the Williams Fork River near its confluence with the Yampa. Based on the <br /> presence of unconsolidated stream-laid holding streams with water availability sufficient for <br /> flood-irrigated agricultural activities, the following two alluvial valleys have been determined to <br /> be alluvial valley floors: <br /> 1. the Yampa River in the Big Bottom area <br /> 2. the Williams Fork River near its confluence with the Yampa River. <br /> Map 35A and Map 52 indicate the locations of AVF well sites and the location of alluvial valley <br /> floors. The Coy well drilled into the alluvium of Flume drainage functions as a point of <br /> compliance well. Four wells are drilled into the Pyeatt alluvium,well J1 is located in the Johnson <br /> drainage alluvium and one of the three GLEV wells in the Deacon drainage reached the alluvium at <br /> the very north east corner of the permit. This GLEV well is located downgradient of any mining to <br /> the east that may occur in the future. These wells constitute an environmental monitoring system <br /> during surface coal mining and reclamation operations continuing until release of all bonds in <br /> accordance with Rule 3 (4.24.4). <br /> Four gulches (No Name, Johnson, Pyeatt, and Flume) are determined not to be alluvial valley <br /> floors based on their absence of water availability sufficient for flood-irrigation or sub-irrigation <br /> agricultural activities. <br /> Potential impacts to the Yampa River AVF resulting from the proposed mining operation are <br /> negligible. Generally,the Yampa River AVF receives very little of its water supply(surface and <br /> ground water) from the proposed mine area. The majority of the flow in the river and subsequent <br /> recharge to the alluvial aquifer derive from the headwaters portions of the drainage, far upstream <br /> from Trapper. The applicant states that the contribution of surface water from the Trapper mine is <br /> insignificant as per page 2-533 of the permit application. <br /> This is substantiated by seepage, runoff, and potentiometric studies in Appendix H of the permit <br /> application. Based on the information presented by the applicant, the Division finds that proposed <br /> surface coal mining operations will not interrupt, discontinue, or preclude farming on the Yampa <br /> River AVF, nor materially damage surface or ground water quantity or quality in systems <br /> supplying the Yampa River AVF (4.24.3(1)), (4.24.3(3), and 2.06.8(5)(a)(ii)). <br /> The potential for impacts from mining to the Williams Fork AVF is also negligible. The <br /> Williams Fork River is located south of the proposed mining area. Almost exclusively, spring <br /> snowmelt comprises the only surface discharge from sediment ponds in the drainages flowing <br /> towards the Williams Fork River. It is likely that much of the discharge from these ponds infiltrate <br /> into the permeable Twentymile Sandstone outcrop prior to reaching the Williams Fork River. <br /> Therefore, the Division finds that the proposed surface coal mining operations will not interrupt, <br /> discontinue, or preclude farming on the Williams Fork AVF, and will not materially damage the <br /> quantity or quality of water in surface or ground water systems that supply the Williams Fork <br /> AVF (4.24.3(1)), (4.24.3(3), and 2.06.8(5)(a)(ii)). <br /> 22 <br />